1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor for use in copiers, facsimile machines, laser printers, and direct digital platemakers. The present invention also relates to a method of manufacturing electrophotographic photoreceptors, and a process cartridge and an image forming apparatus using the electrophotographic photoreceptor.
2. Description of the Background
Recently, the main type of electrophotographic photoreceptor (hereinafter simply “photoreceptor”) has switched from inorganic photoreceptors that use inorganic materials such as selenium, zinc oxide, and cadmium sulfide, to organic photoreceptors that use organic materials. Organic photoreceptors are more advantageous than inorganic photoreceptors in reducing environmental impact and manufacturing cost, and provide more design flexibility. At present, the organic photoreceptors account for close to 100% of the total production of photoreceptors. Recently, attempts are being made to use organic photoreceptors as mechanical components rather than consumable supplies in accordance with increasing momentum toward global environmental protection.
Various attempts have been made to improve the durability of organic photoreceptors. For example, Japanese Patent Application Publication No. (hereinafter “JP-A”) 2000-66424 (corresponding to Japanese Patent No. 4011790) and JP-2000-171990-A have proposed forming a cross-linked resin layer and a zol-gel cured resin layer, respectively, on the surface of a photoreceptor. The former is more productive because the layer is likely to neither fracture nor crack even when an electron transport material is added thereto. In particular, radical-polymerized acrylic resins are advantageous because they are stiff and provide the resultant photoreceptor with high photosensitivity. Because they include plural chemical bonds, such cross-linked or cured resin layers may not be immediately abraded even when a part of chemical bonds are cut by application of mechanical stress.
On the other hand, the main type of electrophotographic toner (hereinafter simply “toner”) is switching from irregular-shaped toner to spherical toner. Spherical toners have an advantage in terms of production of high quality images.
Generally, spherical toners are manufactured through chemical manufacturing processes such as a suspension polymerization process, an emulsion aggregation polymerization process, an ester elongation process, or a dissolution suspension process. Hereinafter, spherical toners may be referred to as “polymerization toners” as appropriate. A typical polymerization toner for use in an electrophotographic image forming apparatus may have an average circularity of from 0.95 to 0.99 and shape factors SF-1 and SF-2 of from 110 to 140. A true sphere has a circularity of 1.0 and shape factors of 100.
Having a uniform shape, each polymerization toner particles has a uniform charge quantity. Therefore, polymerization toner particles develop a latent image into a toner image with high sharpness, resolution, and gradation. In addition to this high developability, polymerization toner particles also have high transfer efficiency. Also, because polymerization toner particles are able to include wax, advantageously, fixing oil is not needed when fixed on a recording medium such as paper. At the same time, disadvantageously, polymerization toner particles are difficult to remove when remaining on a photoreceptor after image development. To solve this problem, a greater amount of external additives is required on the surfaces of the polymerization toner particles, one consequence of which is that the external additives may form a film on the photoreceptor.
In order to more effectively remove residual polymerization toner particles from a photoreceptor, one proposed approach involves applying a solid lubricant (e.g., zinc stearate) to a surface of a photoreceptor to reduce the surface friction coefficient thereof, as described in a technical document entitled “Blade cleaning system for polymerized and small size toner, Hyakutake et al., Japan Hardcopy Fall Meeting, 2001, 24-27”.
However, it is known that the receptivity of a photoreceptor to solid lubricants may affect abrasion rate of the photoreceptor and/or cleanability (removability) of toner, i.e., printing quality. Yet, a technique to improve the receptivity of a highly durable photoreceptor having a cross-linked resin surface layer has not been proposed so far.
JP-2004-61359-A and JP-2007-292772-A disclose a method of evaluating surface roughness of a component for an image forming device, which evaluates local variations in the surface with high sensitivity and accuracy. Specifically, a cross-section curve defined by JIS B0601 is found on the surface of the component and multiple resolution analysis is performed on positional data rows in a surface roughness direction at equally spaced positions on the cross-section curve, and the state of the surface roughness is evaluated at least based on the result.
Advantageously, such a photoreceptor having a surface layer such as a cross-linked resin layer has extremely high durability. On the other hand, disadvantageously, such a surface layer has a low receptivity to solid lubricants and therefore cleanability (removability) of polymerization toners is poor. As a result, at present highly durable photoreceptors having a cross-linked resin surface layer cannot be practically used in combination with polymerization toners.